La Niña is the opposite of El Niño, which are both sides of the coin that make up ENSO, or the El Niño Southern Oscillation. El Niño represents ENSO’s positive “warm” phase, while La Niña is the opposite. The effects of the different phases are wide-reaching and significant, with implications on the weather experienced all across the globe.
La Niña and El Niño typically flip back and forth every one to three years, with some swings of the pendulum more dramatic than others. Most of late 2019 into the first half of 2020 was “ENSO neutral,” or somewhere in between El Niño and La Niña. Then a La Niña started to emerge during the end of summer in 2020, overlapping with the height of a record-breaking hurricane season. Thirty named storms spun up across the Atlantic that season, including a record seven major hurricanes.
After persisting through spring 2021, La Niña took a breather last summer and returned to an ENSO-neutral state before the needle dipped back into the La Niña category in the fall. The 2021 Atlantic hurricane season produced 21 named storms, third most on record.
La Niña persisted through the winter and is still going strong. March proved the most active on record for tornadoes across the Lower 48.
Looking ahead, NOAA is maintaining a La Niña advisory, writing on April 25 that “the tropical Pacific atmosphere is consistent with La Niña.”
They say that La Niña is favored to continue through the summer, with 59 percent odds of remaining into July, August and September. There are 50-55 percent odds of La Niña persisting into the fall.
Since bookkeeping began in 1950, there have been eight “double-dip” La Niñas, including the present. Only two ended up evolving to have a third consecutive La Niña winter. If La Niña does stick around into the late autumn, the possibility of a triple dip La Niña will grow.
There is evidence to suggest that La Niña patterns bolster the risk of severe weather across parts of the South and the southern Plains during tornado season, which peaks in April and May. The bull’s eye of greatest enhancement has historically been centered in Arkansas, though the risk expands across a much broader region.
Part of that stems from the jet stream pattern — the high-altitude river of wind slices across the country west to east, allowing hot and dry weather to crop up in southern areas while cool Canadian air sags south to the north of the jet. In between, the seasons wage war, the resulting clash helping spark thunderstorms. The jet stream simultaneously imparts wind shear, or a change of wind speed and/or direction with height, which helps the storms to rotate.
La Niña could also be a concern in the upcoming hurricane season, which is already projected to be above average. That’s because La Niña patterns are characterized by a subtle weakening of upper-level winds in the tropics. That effectively reduces wind shear, which facilitates the formation of hurricanes. Too much shear can play a game of tug-of-war with a fledgling disturbance, shredding it apart before it can mature into a named system. An absence of that will help more “seeds” to grow into storms.
La Niña also influences the Walker circulation, or a west to east overturning circulation in the equatorial and tropical ocean. Rising or sinking motion in one stretch of the atmosphere must be balanced by the opposite elsewhere. Because La Niña features cool waters in the eastern Pacific, the adjacent air mass in contact is chilled too, resulting in cool air that sinks.
That descent allows air over the Atlantic, which is comparatively buoyant thanks to warmer waters, to rise. In turn, that upward motion spurs more storminess.
There’s no way to know for sure if La Niña will still be as intense at that point — or even around at all — but experts are already sounding the alarms for an active hurricane season. Researchers at Colorado State University expect the season to wind up about 130 percent as active as normal, rivaling or exceeding last year’s above-average season.
If La Niña manages to hold on through the fall and into next year, becoming a true “triple dip” event, it could have the following additional effects:
- Worsening drought conditions in the Southwest and elevating the fire danger since La Niñas tend to result in reduced precipitation in the region
- Raising the odds of a relatively cold, stormy winter across the northern tier of the United States and a mild, dry winter across the South, not unlike this past winter
But looking ahead this far is pretty speculative because computer models are challenged to make accurate ENSO forecasts at this time of year; forecasters refer to this as the spring predictability barrier.
The presence of La Niña and cooler-than-normal ocean waters in the tropical Pacific have helped somewhat lower the average global temperature over the last year or two. 2021 tied as the Earth’s sixth-hottest year on record. If it weren’t for La Niña, the year’s warmth almost certainly would’ve ranked higher.
The first three months of 2022 ranked fifth warmest on record, according to the National Oceanic and Atmospheric Administration. It says 2022 has just a 4.2 percent chance to rank as the warmest year, which is largely due to the La Niña influence. Once El Niño returns, the chances of a record-breaking warm year will increase.